Resumo

ESPINOZA-VILLAVICENCIO, J. Luis et al. Comparison of two models for the estimation of parameters and genetic values of weight in Zebu cattle. Agrociencia [online]. 2008, vol.42, n.1, pp.29-36. ISSN 2521-9766.

Weaning weight and final weight are two traits of interest in beef cattle in Cuba; therefore, it is important to find tools for making selection programs more efficient. The objective of the present study was to compare two genetic models for the estimation of variance components, heritability and the expected difference in progeny (EDP) for weaning weight at seven months (WW7) and final weight at 18 months of age (FW18). Results of a univariate model (UM) were contrasted for these two characteristics against those of a bivariate model (BM), using 59 965 records of WW7 and 7671 of FW 18 of Zebu cattle in Cuba. The information was analyzed with the program REMLF90 of Misztal. The variance components estimated by UM and BM for WW7 were similar and did not modify the magnitude of the estimated heritability of the direct effects (h²_d ; 0.05 vs 0.06). The same occurred with the estimated heritability of the maternal effects (h²_m ; 0.06 vs 0.05). For FW18, the variance components and the h²_d presented important changes. The h²_d was higher with BM (0.25) than with UM (0.19). The genetic correlation between the direct effect and the maternal effect for WW7 was -0.36 in UM and -0.07 in BM. The differences between the best and the worst bulls in the EDP for WW7 were similar for the direct and maternal effects when both types of analyses were used. For FW18 the difference of the EDP between the worst and the best bull was 31.8 kg with UM and 38.8 kg with BM. The use of a bivariate animal model makes it possible to increase the genetic improvement of FW18, with respect to a model that includes each trait independently.

Palavras-chave : Zebu cattle; genetic parameters; weaning weight; final weight; genetic values.

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